A method is known to typically separate nitrogen from a gas containing nitrogen, methane, ethane, or the like by use of a rubber membrane as a type of organic membrane (reference is made to Patent Literature 1). This method obtains a nitrogen-depleted gas and a nitrogen-enriched gas as a result of selective permeation of methane and ethane in the gas by use of a first rubber membrane and a second rubber membrane.
The Patent Literature 1 is Japanese Patent Application Laid-Open No. 2010-202875.
Furthermore a method has been proposed (reference is made to Non-Patent Literature 1 and 2) to obtain a nitrogen-depleted gas and a nitrogen-enriched gas as a result of selective permeation of nitrogen from a mixed gas of nitrogen and methane by use of an inorganic membrane such as a CHA zeolite membrane or DDR zeolite membrane.
The Non-Patent Literature 1 is “Influence of propane on CO2/CH4 and N2/CH4 separations in CHA zeolite membranes, Journal of Membrane Science 473, (2015) 201-209” (Ting Wu (six others)). The Non-Patent Literature 2 is “Separation and permeation characteristics of a DD3R zeolite membrane, Journal of Membrane Science 316 (2008), 35-45” (J. van den Bergh (four others)).